1. Field of the Invention
The present invention relates to the color improvement of alkyl vanadates.
2. Description of the Prior Art
Various methods are known for the preparation of alkyl vanadates. U.S. Pat. No. 4,014,912 to R. L. Muntz et al. describes reaction of vanadium oxytrichloride with an alcohol in the presence of ammonia and a hydrocarbon solvent with the later addition of dimethyl sulfoxide. The reaction is conducted under an inert gas atmosphere to prevent decomposition of the product. A variation of this process, in which an amide is added, rather than dimethyl sulfoxide, is described in U.S. Pat. No. 4,014,911 to R. L. Muntz et al. In this patent it is suggested that a stream of inert gas be passed through the reaction mixture to sweep out a portion of the hydrogen chloride by-product released by the reaction.
Alkyl vanadates are formed by reaction of vanadium pentoxide and an alkyl alcohol in a process described in U.S. Pat. No. 3,657,295 to D. R. McCoy. Once again, this patent indicates use of an inert atmosphere to prevent decomposition of the product.
In U.S. Pat. No. 3,987,074 to R. Haase et al. alkyl vanadates are described as being prepared by reaction of vanadium pentoxide and an alcohol in the presence of a particular orthoester to assist in the removal of by-product water. This patent indicates that vanadium pentoxide reagent remaining after the reaction can be regenerated and restored to full reactivity by thermal treatment, e.g., at 300.degree.-400.degree. C., under air or oxygen.